This application is base upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-086230, filed Mar. 23, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a radio communication apparatus for controlling a transmission power in a variable way in accordance with a reception power and a transmission power controlling apparatus used in the radio communication apparatus.
2. Description of the Related Art
FIG. 1 is a block diagram showing a radio communication apparatus provided on an existing mobile telephone terminal.
In the radio communication apparatus, a transmit signal applied from a modulator, not shown, is processed by a variable amplifier 1, up-converter 2 and bandpass filter 3 and a power amplifier 4 to provide a transmit signal of a state capable of radio transmission. The transmit signal is passed through a duplexer 5 and antenna switching unit 6 normally to a standard antenna 7 where it is radiated as a radio wave.
An external antenna 17 can be connected to the antenna switching unit 6. Whether or not the external antenna 17 is connected is monitored by an antenna detection circuit 8. If the external antenna 17 is connected, the external antenna 17 is selected by the antenna switching unit 6 under control of the antenna detection circuit 8. With the external antenna 17 thus connected, the transmit signal outputted from the power amplifier 4 is supplied through the duplexer 5 and antenna switching unit 6 to the external antenna 17 where it is radiated as a radio wave.
A radio wave is received by the standard antenna 7 or external antenna 17 as a received signal. The received signal is sent through the antenna switching unit 6 and duplexer 5 to a receiver 9. The received signal is converted to a digital-like baseband signal by the receiver 9 and an A/D converter 10 and then supplied to a baseband processing section not shown.
The transmission power can be controlled by a gain of the variable amplifier 1 and it is basically determined by a reception power. That is, it is considered that a greater reception power ensures a better state of a radio channel. Therefore, even if the transmission power is made lower, an adequate communication quality can be maintained and the transmission power can be lowered. If, on the other hand, a reception power is smaller, then the transmission power is increased so as to secure an adequate communication quality.
Therefore, a designation value generation section 11 monitors an output of the A/D converter 10 and determines a gain capable of achieving a transmission power corresponding to the reception power. A gain control section 12 basically outputs a gain controlled value for allowing an amplification to be done, by the variable amplifier, with the gain determined by the designation value generation section 11. Then, the gain controlled value is converted by the D/A converter 13 from a digital form to an analog version to obtain a gain control signal. The gain control signal is applied to a variable amplifier 1.
By a first loop thus constituting an open loop, a basic transmission power control is carried out.
If, however, the transmission power is so controlled by the first loop only, when a reception power involves a largely lowered state, control acts toward largely increasing a transmission power. And there is a risk that the transmission power will exceed a maximum transmission power determined legally or from a standpoint of a system involved.
In order to stabilize the transmission power to a maximal transmission power, therefore, a second loop is provided which comprises a detection circuit 14, reference circuit 15 and comparator 16. If a gain determined by the designation value generation section 11 exceeds a given threshold value, the transmission power control by the first loop is stopped and the transmission power control by the second loop is carried out.
As a result, the reception power/transmission power relation is as shown in FIG. 2 and the transmission power is restricted by the maximum transmission power. FIG. 2 shows an example in which the maximal transmission power is 21 dBm.
The gain determinations by the first and second loops are done under a condition based on the use of the standard antenna 7 in either case. However, there are often the cases where a loss differ between the standard antenna 7 and the external antenna 17. Stated in more detail, the external antenna 17 is often greater in a loss than the standard antenna 7 from the standpoint of its longer cable length, etc. Under the situation above, even if the gain of the variable amplifier 1 is the same, there occurs the difference in transmission power between using the standard antenna and using the external antenna 17.
In the case of performing the transmission power control by the first loop, the difference in the loss appears also in the reception power due to the difference between the antennas used. In order to compensate the difference in the loss, the setting of the gain is carried out. Stated in more detail, as shown in FIG. 2, suppose that the reception power at the time of using the standard antenna 7 is PRX and hence the operation point is located at a point A and control is made such that the transmission power becomes 16 dBm. In this case, suppose that the external antenna 17 is connected and the loss are increased to 2 dBm. Then the reception power detected by the designation value generation section 11 is lowered to PRXxe2x88x922 as indicated by an arrow B. And the designation value generation section 11 increases a gain so as to increase the transmission power to 18 dBm as indicated by an arrow C. And the operation point is varied to a point D. As a result, an output level from the variable amplifier 1 is increased up to a level corresponding to the transmission power of 18 dBm. Since a loss by the external antenna 17 is involved as indicated by an arrow E, the actual transmission power becomes 16 dm, so that the operation is performed at the same point A as at the time of using the standard antenna 7.
As shown in FIG. 3, suppose that the operation point at the time of using the standard antenna 7 is located at a point F near a threshold value xe2x80x9c21xe2x80x9d. In this state, suppose that the external antenna 17 is connected and the loss is 2 dBm increased. Then the reception power detected by the designation value generation section 11 is lowered to PRXxe2x88x922 as indicated by an arrow G. In this case, the designation value generation section 11 tries to increase a gain so as to increase the transmission power to 22 dBm, but it exceeds the threshold value. And the second loop operates. That is, the transmission power at the time of using the standard antenna 7 is suppressed under the action of the second loop to a gain of 21 dBm and the operation point becomes a point I. Then, as indicated by an arrow J, a loss by the external antenna 17 is involved and the actual transmission power becomes 19 dBm. And the operation is done at an operation point K different from that at the time of using the standard antenna 7. For this reason, the transmission power is lowered.
As set out above, the conventional apparatus was not able to properly control the transmission power at all times.
The present invention is achieved with the above-mentioned situations in view and, accordingly, the object of the present invention is to provide an apparatus which can properly control a transmission power even if either of a standard first antenna and external second antenna is used.
In one aspect of the present invention, there is provided a radio communication apparatus for varying a transmission power in accordance with a reception power in a range not exceeding a predetermined maximum transmission power, comprising: a variable amplifier configured to amplify a transmit signal, the gain of the variable amplifier being variable upon amplification; a first antenna; an antenna switching unit detachable to a second antenna and configured to select one of the first and second antennas if the second antenna is attached to the apparatus; and a transmission power controller configured to control the gain of the variable amplifier such that
if the antenna switching unit selects the first antenna and a standard gain determined in accordance with the reception power does not exceed a first predetermined limit value determined by the maximum transmission power and power loss at the first antenna, the gain of the variable amplifier is set to the standard gain;
if the antenna switching unit selects the first antenna and the reference gain exceeds the first limit value, the gain of the variable amplifier is set to the first limit value;
if the antenna switching circuit selects the second antenna and the standard gain does not exceed a second predetermined limit value determined by correcting the first control value based on a difference between a power loss at the first antenna and a power loss at the second antenna, the gain of the variable amplifier is set to the standard gain; and
if the antenna switching unit selects the second antenna and the standard gain exceeds the second limit value, the gain of the variable amplifier is set to the second limit value.
In another aspect of the present invention, there is provided a transmission power controlling apparatus supplied to a radio communication apparatus adapted to vary a transmission power in accordance with a reception power in a range not exceeding a predetermined maximum transmission power and comprising a variable amplifier configured to amplify a transmit signal, the gain of the variable amplifier being variable upon amplification, a first antenna and an antenna switching unit arbitrarily connectable to a second antenna and configured to select one of the first antenna and second antenna, the transmission power controlling apparatus controlling the transmission power at the radio communication apparatus and comprising a transmission power controller configured to control a gain of that variable amplifier such that
if the antenna switching unit selects the first antenna and a reference gain determined in accordance with the reception power does not exceed a first predetermined limit value determined by the maximum transmission power and power loss at the first antenna, a gain of the variable amplifier is set to the reference gain;
if the antenna switching unit selects the first antenna and the reference gain exceeds the first limit value, the gain of the variable amplifier is set to the first limit value;
if the antenna switching unit selects the second antenna and the reference gain does not exceed a second predetermined limit value determined by correcting the first limit value based on a difference between a power loss at the first antenna and a power loss at the second antenna, the gain of the variable amplifier is set to the reference gain; and
if the antenna switching unit selects the second antenna and the reference gain exceeds the second limit value, the gain of the variable amplifier is set to the second limit value.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.